1. Technical Field
The present invention relates to an input device that detects the approach of an operating body, such as a user's finger, using a variation in capacitance, and more particularly, to an input device capable of detecting the approach of a plurality of operating bodies.
2. Related Art
Various electronic apparatuses, such as personal computers, are provided with input devices including flat scanning pads. In this type of input device, when a finger touches the scanning pad, the coordinates of the contact position of the finger with the scanning pad are detected. It is possible to perform an input operation on various electronic apparatuses by detecting the contact position of the finger.
In general, the input device according to the related art can detect only one contact point of the finger with the input pad. However, in the electronic apparatuses, in some cases, when a plurality of fingers simultaneously touch the input pad, it is necessary to individually detect the contact positions of the fingers.
JP-A-7-230352. and JP-A-8-16307 disclose input devices capable of detecting the contact positions of a plurality of fingers with the input pad.
The input pad disclosed in JP-A-7-230352 includes a plurality of X direction electrodes and a plurality of Y direction electrodes, and AC signals are supplied to the X direction electrodes and the Y direction electrodes. When a finger approaches an intersection of any one of the X direction electrodes and any one of the Y direction electrodes, the intersection capacitance between the X direction electrode and the Y direction electrode is attenuated, and the level of the AC signal between the X direction electrode and the Y direction electrode is lowered. When a plurality of fingers approach, it is possible to individually detect the intersections between the electrodes approached by the fingers by sequentially supplying the AC signals to the X direction electrodes and the Y direction electrodes.
When a plurality of fingers touch the input pad, the input device disclosed in JP-A-8-16307 can individually detect the contact positions of the fingers using a surface acoustic wave touch plate or a two-dimensional optical sensor array touch plate.
The input device disclosed in JP-A-7-230352 detects a variation in the intersection capacitance between the X direction electrode and the Y direction electrode. Therefore, in order to individually detect the approach positions of a plurality of fingers, it is necessary to sequentially monitor the intersection capacitances at the intersection between all the electrodes. In order to meet the necessity, it is necessary to individually detect a variation in the level of a signal between a selected X direction electrode and a selected Y direction electrode and sequentially perform the detecting operation on all of the X direction electrodes and the Y direction electrodes. In such a detecting method, the load of a detecting circuit is increased, and it is necessary to sequentially examine a variation in the intersection capacitances of all the intersections. Therefore, it takes a long time to scan all the intersections of an input panel and it is difficult to rapidly perform a detecting operation.
The input device disclosed in JP-A-8-16307 is a surface acoustic wave type or a two-dimensional optical sensor array type. Therefore, the touch plate has a complicated structure and is expensive, and a detecting circuit is also complicated, which is not practical.
These and other drawbacks exist.